The present invention relates to a device for injecting material in a plastic state into a moulding cavity, comprising particularly:
a distributor of material in a plastic state, comprising at least one outlet for material in a plastic state, placed along a pre-set axis,
an injection nozzle comprising at least one component which is connected to the distributor by a detachable connection means and defines for the injection nozzle a front surface configured in such a way that it can become integral with the moulding cavity, the injection nozzle comprising at least one channel for material in a plastic state, placed along said axis and placed in a fluid relationship with said outlet, and emerging in said front surface,
controlled means of blanking said channel.
It relates to such a device whatever the design furthermore of the distributor and of the injection nozzle and their arrangement relative to a mould defining the moulding cavity, it being understood that the position of the axis common to the distributor material outlet and to the injection nozzle and the position of the front surface of the latter relative to the moulding cavity are understood by reference to a xe2x80x9chotxe2x80x9d state of the injection device and of the mould, namely the state they are in when they are brought to the temperature which they present under material injection conditions, with expansion phenomena taken into account.
A man skilled in the art knows that it is particularly important that when hot, the front surface of the nozzle is as perfectly integral as possible with the moulding cavity if it is required to avoid the presence of a space or an awkward contour, corresponding to this front surface, on the moulded component in the cavity. This concern is particularly significant when the shape of the cavity, in other words the shape of the component to be moulded, leads to the front surface of the nozzle being given a shape and an orientation different from a plane shape perpendicular to the common axis of the nozzle and the material outlet.
In the current state of the art, the nozzle is connected in a detachable way to the distributor by mutual screwing by means of a complementary screw thread and female screw thread provided respectively on one and in the other.
More exactly, in the frequent case in which the injection nozzle comprises particularly a nozzle end piece defining the front surface and a nozzle body inserted between the distributor and the nozzle end piece and connected to one and the other by a respective detachable connection means and in the equally frequent case in which the distributor comprises a channel for assembling an injection nozzle support, provided along the material outlet axis, and an injection nozzle assembly support, defining this outlet and connected to the distributor and to the injection nozzle by a respective detachable connection means, each of these detachable connection means is constituted by a female screw thread and a screw thread centred on the material outlet axis and provided respectively in one and on the other of the components to be connected in a detachable way.
This detachable connection mode does not in fact give complete satisfaction in the concern to make the front surface of the injection nozzle as integral as possible with the moulding cavity.
Indeed, the screwing relationship, along the material outlet axis, of the different components of the injection device directly connects the position of the front surface along this axis and its orientation around it.
To be sure, by accurate machining and by providing stops to restrict screwing, the front surface can be made to be as integral as possible with the cavity during a first assembly of the injection nozzle on the distributor, which is already tricky but may be corrected by adjustment after the first assembly if the precaution is taken initially to oversize the nozzle in the axial direction, but it is in practice impossible to recover the same conjugation of axial and angular positions of the front surface relative to the cavity when the nozzle is reassembled on the distributor after disassembly.
Stops restricting screwing may to advantage consist of annular plane bearing ends, of revolution around the material outlet axis, also providing the seal between the different components, but the sealing thus obtained during a first assembly is not necessarily recovered during reassembly after disassembly. Indeed, at reassembly, the concern to make the front surface of the nozzle as integral as possible with the cavity may be incompatible with that of establishing a seal contact between the bearing ends; in other words, it is difficult to seal in a durable way the screw thread and the female screw thread relative to the channel of material in a plastic state, considering the generally high pressure which this material generally reaches when it passes through the distributor and through the nozzle, and the material in a plastic state may insinuate itself into the female screw thread and screw thread and hamper operations of disassembly and re-assembly.
The purpose of the present invention is to overcome these drawbacks and, to this end, the present invention proposes a device of the type specified in the preamble, characterised in that said detachable connection means comprises:
means of indexing the angular position of said front surface in relation to the distributor, around said axis, and
locking means fixing said front surface in relation to the distributor in the relative angular position imposed by the indexing means.
More exactly, when the injection nozzle comprises particularly a nozzle end piece defining said front surface and a nozzle body inserted between the distributor and the nozzle end piece and connected to one and the other by a respective connection means one of which, at least, is a detachable connection means, this detachable connection means, where necessary respective, comprises, according to the invention:
means of indexing in a relative angular position around said axis,
mutual locking means in the relative angular position imposed by the indexing means.
This may be the case particularly when, according to an embodiment of the device according to the invention, the distributor comprises a nozzle body assembly channel, provided along said axis, and the nozzle body is engaged coaxially into said channel and defines said outlet.
Likewise, when, according to another embodiment, the distributor comprises an assembly channel for an injection nozzle assembly support, provided along said axis, and an injection nozzle assembly support, engaged coaxially in said channel, defining said outlet and connected to the distributor and to the injection nozzle by a respective connection means one of which, at least, is a detachable connection means, this detachable connection means, where necessary respective, comprises according to the invention:
means of indexing in a relative angular position around said axis, and
mutual locking means in the relative angular position imposed by the indexing means.
A man skilled in the art will easily understand that, so long as the distributor and the nozzle, and more exactly their different components, and their indexing means have been appropriately designed and manufactured in such a way that at first assembly of the nozzle on the distributor, the front surface may become as integral as possible with the moulding cavity, the presence of the indexing means makes it possible to recover this position without difficulty after each disassembly of the nozzle.
This characteristic design of the invention is combined to advantage with the fact that the seals between the nozzle and the distributor, and more exactly, in the case of the embodiments previously mentioned, between the nozzle end piece and the nozzle body, the nozzle body and the distributor or more exactly, according to the case, the nozzle body and the nozzle assembly support, and this support and the distributor, are made by mutual support, along the direction of the material outlet axis, of bearing ends annular of revolution around this axis, plane and perpendicular to it, in the same way as in the prior art. Indeed, the independence, which it is possible to obtain through implementing the present invention, between the position of the front surface along the axis and its annular position around it allows the required seal to be provided even after disassembly and reassembly of the nozzle.
In a particularly straightforward way, the indexing means may comprise cotter pinning parallel to the material outlet axis, which cotter pinning may be common to the means of indexing the nozzle assembly support in an angular position relative to the distributor and to the indexing means of the injection nozzle in an angular position relative to the assembly support when such an assembly support is provided and connected to the distributor by a connection means comprising such indexing means and mutual locking means in the relative angular position imposed by these indexing means.
The mutual locking means may comprise to advantage mutual clamping by a ring annular of revolution around the material outlet axis, said ring being screwed by rotation around the latter onto a flange of one of the components to be assembled by tightly gripping with it a flange of the other component; it will be observed that, in a way sought after in accordance with the present invention, the degree of screwing of the ring has no influence on the axial position and the angular position of the front surface, and simply conditions the mutual support force, along the axis, of the above-mentioned sealing bearing ends.
When, in a way known per se, the controlled blanking means comprise at least one blanking pin mounted with axial sliding inside the injection nozzle channel, between a blanking position of the latter and an open position of the latter, and controlled means to make the pin slide from one to the other of said positions, located on the opposite side from the injection nozzle relative to the distributor along said axis and comprising controlled drive means, a component for transmitting motion between the drive means and the pin, placed in the axial extension of the latter, and a detachable connection means of said component and of the pin in an axial direction, allowing a relative free rotation around said axis, the device according to the invention comprises to advantage means for indexing the pin relative to the distributor in a preset relative angular position around said axis, for example in the form of cottering parallel to it.
For example, when the injection nozzle is assembled on the distributor by means of an assembly support according to an embodiment mentioned above, the means for indexing the pin relative to the distributor, for example cottering parallel to the axis, are to advantage constituted by means for indexing the pin relative to the injection nozzle assembly support. When, according to another embodiment mentioned above, the nozzle comprises a nozzle body engaged coaxially in an assembly channel provided in the distributor, the means for indexing the pin relative to the distributor, for example by cottering parallel to the axis, are to advantage constituted by means for indexing the pin relative to the nozzle body.
It is thus possible to ensure that the blanking pin also occupies a preset angular position not only on first assembly of the nozzle on the distributor but also after disassembly followed by reassembly, in other words still engages by the same zones with the same zones of the nozzle, particularly with a counterpart provided on the latter to provide blanking by engagement with the pin.
Additionally, this indexing of the blanking pin, by immobilising the latter against rotation relative to the distributor, makes it possible to provide the connection of the pin with the motion transmission component by a means screwed coaxially onto or in the pin, respectively an extension integral with it, without encountering for all that any difficulty in screwing or unscrewing this means during the initial assembly and maintenance operations.
However, such an arrangement is particularly advantageous when, to avoid the formation of an injection sprue on the moulded component in the cavity, the blanking pin has a front surface, configured in such a way that it can become integral with the moulding cavity in the blanking position, in a way known per se. Indeed, it is then possible to be sure that, at initial assembly and at any reassembly after disassembly, the front surface of the pin is appropriately orientated, in the same way as the front surface of the nozzle, so as to become as integral as possible with the cavity.
Such an arrangement is also particularly advantageous when, in a way known per se, in order to practise a multi-material injection, the injection nozzle channel is subdivided into several different elementary channels which are distributed angularly around the axis and each of which corresponds to one of the materials to be injected and may be blanked or opened in a controlled way by a respective pin, the different pins corresponding to the different elementary channels being a mutually juxtaposed along a plane including the axis or half-planes defined by the latter. Naturally, in such a case, the distributor comprises several material outlets distributed around an axis which is that of the nozzle.
Other characteristics and advantages of the invention will emerge from the description given below, in relation to the currently preferred example of implementation, and the appended drawings, which are an integral part of this description.